Thus, even in control cells, an increase in the angle between the centrosome position at NEBD and the spindle position at the metaphase anaphase transition appeared to correlate with the occurrence of anaphase chromosomes bridges (red dots in Figures 7BC7D and bar plots in Figure?7E). 10m. mmc4.mp4 (4.4M) GUID:?AFF8A148-D891-41D7-BDED-79D845164E00 Video S4. Related to Figure?3E Centrosome separation following STLC washout in STLC/1NM-PP1 arrested U2OS cdk1as cells (as in Video S2). GFP-alpha-Tubulin is shown in green and RFP-PACT in red. The scale bar indicates a length of 10M, time is indicated as hh:min on the top left. Left panel STLC wash out in control cells, right panel STLC washout in Cytochalasin D treated cells. mmc5.mp4 (8.8M) GUID:?4028D2E7-43E1-4844-A8E4-75DB9DF16FF5 Video S5. Related to Figure?4A Centrosome congression toward the nuclear centroid. Centrosomes (red and blue) were tracked relative to nuclear mask (yellow) and cell mask (white) and distances from nuclear centroid (yellow dot) and cellular centroid (white dot) were calculated for each frame. Note the significant difference of movement between the two centrosomes and overlap of the meeting point with the nuclear centrosome. mmc6.mp4 (2.6M) GUID:?647C051A-2FF0-4500-95B9-D7998E572DE3 Video S6. FLJ39827 Related to Figure?5A Actin/MT interactions during centrosome congression in U2OS cdk1as cells that were treated for 16 hours with 2M 1NM-PP1. 5M STLC was added at the start of the imaging sequence (as in Video S3). GFP-alpha-Tubulin is shown in green and SiR-Actin in red. The scale bar indicates a length of 10M, time is indicated as hh:min on the top left. Note the MT reaching toward the perinuclear actin ring. mmc7.mp4 (2.9M) GUID:?0046F21B-C791-4501-ACFD-14B392A04376 Video S7. Related to Figure?5C Prophase specific perinuclear actin DBU formation in asynchronous U2OS cells, see also Figure?7G. GFP-alpha-Tubulin is shown in green and SiR-Actin in red. The scale bar indicates 10m, time is indicated as hh:min on the top left. Note the transient formation of a perinuclear actin structure in prophase during time-frames 9:51 to 10:12 mmc8.mp4 (4.5M) GUID:?4D14981F-54C1-45AA-B7CD-47159F58C461 Video S8. Related to Figures 6C and 6F Effects of GFP-FHOD(1-339) expression on centrosome congression (left panel, as in Video S3) and separation (right panel, as in Video S2) in 1NM-PP1 arrested U2OS cdk1as cells. GFP-alpha-Tubulin is shown in white, the scale bar indicates 10m, time is indicated as hh:min on the top right. mmc9.mp4 (4.4M) GUID:?A17030E8-7002-4ED2-A12D-B8E43566E373 Document S1. Figures S1CS5 mmc1.pdf (1.5M) GUID:?0FC22FFD-4518-40A2-AC2C-EA70F98F8655 Document S2. Article plus Supplemental Information mmc10.pdf (10M) GUID:?D75AF1D6-2F18-4B77-8AB1-FDECC588D68F Data Availability StatementOriginal source code for image segmentation and analysis is available at https://github.com/fabio-echegaray/contour-field and https://github.com/fabio-echegaray/centrosome-tracking. Summary Centrosome separation in late G2/ early prophase requires precise spatial coordination that is determined by a balance of forces promoting and antagonizing separation. The major effector of centrosome separation is the kinesin Eg5. However, the identity and regulation of Eg5-antagonizing forces is less well DBU characterized. By manipulating candidate components, we DBU find that centrosome separation is reversible and that separated centrosomes congress toward a central position underneath the flat nucleus. This positioning mechanism requires microtubule polymerization, as well as actin polymerization. We identify perinuclear actin structures that form in late G2/early prophase and interact with microtubules emanating from the centrosomes. Disrupting these structures by breaking the interactions of the linker of nucleoskeleton and cytoskeleton (LINC) DBU complex with perinuclear actin filaments abrogates this centrosome positioning mechanism and causes an increase in subsequent chromosome segregation errors. Our results demonstrate how geometrical cues from the cell nucleus coordinate the orientation of the emanating spindle poles before nuclear envelope breakdown. (Faivre-Moskalenko and Dogterom, 2002, Holy et?al., 1997, Pinot et?al., 2009), (Letort et?al., 2016), and in fungi (Brito et?al., 2005, Tran et?al., 2001). Moreover, MCAK(mitotic centromere-associated kinesin, Kif2C/kinesin-13)- and Kif18B-(kinesin-8)-dependent MT DBU depolymerization contributes to bipolar spindle formation when Eg5 is inhibited, suggesting an antagonism between spindle pole separation and MT polymerization in mitosis (van Heesbeen et?al., 2017). The involvement of Tiam-1/Rac and p21-activated kinase signaling in opposing Eg5 could imply cross-talk with the cell cortex in this mechanism (Whalley et?al., 2015, Woodcock et?al., 2010). Accordingly, we have previously reported that inhibiting Cdk1 in chicken DT40 cells results in slow centrosome separation that is constrained by cortical MT pressure (Smith et?al., 2011). DT40 cells.